ACKNOWLEDGMENTS 
A PREFACE is needless for a book of this kind, which 
needs no explanation and could be saved by no excuses; and 
I may substitute for it an Acknowledgment of Gratitude 
due to those who have helped me, much to the advantage of 
the reader. 
Foremost among them is Mr. George P. Brett, President 
of The Macmillan Company, who has placed at my disposal 
every facility for, and put no obstacles in the way of, my 
making the best book within my power. If I have not suc- 
ceeded, it is not the fault of my publishers. 
Next I wish to recognize gratefully the important service 
rendered the book by Dr. W. D. Matthew, Associate Curator 
of Vertebrate Paleontology in the American Museum of 
Natural History in New York, in giving me the benefit of 
his eminent knowledge of extinct mammals and in super- 
vising those pages of the book relating to them. The reader 
and myself are similarly indebted to Professor Henry F. 
Osborn, Curator of Vertebrate Paleontology in the American 
Museum of Natural History ; to Dr. Daniel G. Elliot, Director 
of the Field Columbian Museum, Chicago; to Mr. William T. 
Hornaday, Director of the New York Zoological Park, and 
to certain others, for the criticism and approval of parts of 
the work in which they were especially interested and well 
informed. 
The liberality of the New York Zoological Society has 
enabled me to place before the reader many of the original 
and admirable pictures of animals made by the Society’s 
Photographer, Elwin R. Sanborn; while other excellent illus- 
vii 
